Electric discharge lamps

ABSTRACT

Electric discharge lamps having the fill of mercury and an innert-gas such as argon added with gallium and a halide such as iodine and bromine to make the light output rich in the vicinity of 400 mu wave length band to be adapted particularly for the light source for blueprinting, photolithography, in which gallium is added far excessive to the chemical equivalence for the gallium halide so that the gram-atom number ratio of gallium to the halide ranges from 0.5 to 3.0, whereby the satisfactory light output of the prior art type mercury lamp having the additive fill of gallium halide is kept and the disadvantage thereof, namely inevitably higher starting and reigniting voltages can be avoided.

D United States Patent [1 1 [111 3,772,557 Yoshida et al. I Nov. 13,1973 1 ELECTRIC DISCHARGE LAMPS [75] Inventors: Yasuo Yoshida, Urawa;Katsuhiro Primary [flake Kawai, Kita Adachi gun, saitama; AssistantExammer-Darwm R. Hostetter Hiroshi Namiki, Omiya, all of Japan [73]Assignee: lwasaki Denki Kabushiki Kaisha, I

Tokyo Japan [57] ABSTRACT [22] Filed: May 11, 1972 Electric dischargelamps having the fill of mercury and an innert-gas such as argon addedwith gallium and a PP N05 252,229 halide such as iodine and bromine tomake the light output rich in the vicinity of 400 mu wave length band[30] Foreign Application Priority Data to be adapted particularly forthe light source for blue- Ma H 1971 Ja an 46,30850 printing,photohthography, in which gallium 18 added y p far excessive to thechemical equivalence for the gallium halide so that the gram-atom numberratio of gal- 313/229 26324 3; lium to the halide ranges from 0.5 to3.0, whereby the Fieid 227 satisfactory light output of the prior arttype mercury a c lamp having the additive fill of gallium halide is keptand the disadvantage thereof, namely inevitably higher [56] UNlTE S fr S::fl ENTS starting and reigniting voltages can be avoided. 3,521,111 71970 Tsuchihashi et a]. 313 229 2 Claims, 3 Drawing Figures ,3 D e a i lt D O I i I O GRAM ATOM RATIO (Ga/I) PATFNIEU Rev 1 3 ms SHEET 1 CF 2 C?lllllllllllllllll Ill-l.

B lllllllllll [I3 0 O o O O o 3 2 1 GRAM ATOM RATIO (Ga/I) O O O o 2 1ll 3L PDPPDO FIG:

ELECTRIC DISCHARGE LAMPS The invention relates to electric dischargelamps of mercury vapour added with usual inert-gas as well as galliumand a halogen such as iodine, bromine, and more particularly to animprovement of the lamps of such type to be made more suitable as thelight source for photochemical reactions such as exposure ofphotosensitive agent for copier, photolithography and the like.

As well known, the photosensitive agents are particularly highlysensitive to the light of wave length band ranging from 380 to 420 mu,although it may be varied more or less depending on the kind of theagents.

Hithertofore the so-called mercury lamps, above all of high pressuremercury vapour type, have been used as the light source for thosepurposes. These mercury lamps, however, have their highest light outputin the range of 365 my. wave length so far as the band effective forphotochemical reactions is concerned. Or in other words, a substantialportion of the radiation energy has been wasted. These conventionaldischarge lamps, thus, are not satisfactory in the efficiency of theexposure of the photosensitive papers and the like.

It has been already proposed in order toovercome these faults to addgallium iodide (Gal to mercury and the inert-gas in the envelope,whereby the light output may be increased or strengthened in bands of403 my. and and 417 my. which correspond to the particular spectra ofgallium. This recently developed lamp having an additional fill ofgellium triiodide can radiate the light rich in the band approximatelyof 400 my. so that it is surely satisfactory as the light source forexposing the copier sensitive papers and the like. It is still notsatisfactory, however, in that relatively high voltages are necessaryfor starting and reigniting and that the voltages are apt to be raisedas the lamp is used, although this is inevitable more or less in case ofusing an additive in the form of a metal halide. The cause has beenacknowledged possibly due to impurities such as water and hydrogeninevitably mixedly introduced in the envelope together with the halogenor the metal halide as well as due to free halogen to be generated inthe envelope. In order to avoid this disadvantage, it may be taken intoconsideration to decrease the amount of the halogen, above all iodine tobe added, but it has been taken a strong hold of the persons skilled inthe art that the halogen must be added in the amount of chemicalequivalence relative to gal lium. Even if the manufacturers take accountof the possible weighing error, thus, the halogen has been added in theamount slightly less than the chemical equivalent.

We, the inventors, have exhausted various experiments to findunexpectedly against this technical common sense that it is possible todecrease the amount of the halogen such as iodine and bromine relativeto gallium considerably from the chemical equivalent thereof wherebysaid fault can be completely avoided without lowering the light outputin the wave length band of 380 my. to 420 mu.

The invention shall be explained in more detail in reference to thedrawing, in which;

FIG. 1 is a diagram in which the light output of the mercury lamp havingthe fill of mercury vapour and argon added with gallium and iodine isshown in percentage in the ordinate relative to 100 percent in the wavelength band of 380 mp. to 420 mp. of the light output of the mercurylamp just same but involving no gallium nor iodine; and the gram-atomnumber ratio of gallium to iodine with varying the amount of the formerrelative to the fixed amount of the latter is taken in the abscissa;

FIG. 2 is'a diagram in which the light output of the two mercury lampshaving filling additives of gallium and iodine, one in the gram-atomratio of 1:3 while the other of 1:1 with holding the gallium amount tobe the same, is taken in the ordinate in percentage relative to percentof the light output in the wave length band of 380 my. to 420 mg. of themercury lamp just same but without said additional fill; and the amountof gallium filled in the radiation envelope is shown in the abscissavariously changed in gram-atom per 1 cc. of the inner capacity of saidenvelope;

FIG. 3 is a cross-sectional view of a mercury discharge lamp embodyingfeatures of the invention.

In FIG. 3 a field envelope 10 is filled with mercury and an inert gas towhich the components discussed have been added. A pair of electrodes 12and 14 project through the envelope 10.

The inventors made experiments to obtain the results illustrated in FIG.1 with using the 2 KW mercury lamp having a radiation envelope of 15 mmdiameter and 200 mm effective length filled with 60 mg mercury and 15 mgargon as well as iodine in the amount of 0.98 X 10 gram-atom per 1 cc.of the inner capacity of said envelope to which gallium was added in avaried amount. In said figure, point A represents the light output incase where gallium was added relative to iodine in the gram-atom numberratio of 1:3 according to the prior art or the common sence in thistechnical field. It illustrates that said recently developed mercurylamp could improve the light output effective for the photochemicalreaction two times in comparison with such an old mercury lamp as havingthe usual inert-gas but no additive referred to above. Points B, C and Drespectively show the light outputs of the mercury lamps having galliumfilled in the respective amounts relative to iodine in 1.5, 3.0 and 9.0times the chemical equivalence to form gallium triiodide. As referred toabove, it has been considered, although it goes without saying when theadditional filling is introduced in the form of said compound, thatgallium and iodine added respectively in the form of the element cancontribute said improvement finally in the form of gallium triiodide inthe envelope. If gallium should be useful merely in the form of saidcompound, addition or presence of such excessive amounts of gallium as1.5, 3.0 and 9.0 times the chemical equivalent to iodine would at leastnot improve the light output characteristics or rather adversely affectthereon.

The results of our experiments showed, unexpectedly or against theconventional understanding, that such points B, C and D were all in farhigher levels than point A. The mercury lamp having the additional fillconsisting of gallium and iodine in the gram-atom number ratio of 1:2showed the light output of 2.5 times the old mercury lamp, as shown bypoint'B. The output was made 3 times in fact when said ratio was of 1:1,beyond expectation as shown by point C in FIG. 1. This unexpectedlywonderful result was still attained even if the amount of gallium wasincreased up to even 3 times the iodine content in the gram-atom numberratio, as shown by point D. The facts referred to above undoubtedlyshows that gallium and iodine filled in the lamp envelope act on thephotochemically effective light radiation at least not only in the formof gallium triiodide but also in combination of the lesser amount ofiodine with gallium, although correct explanation on the phenomenon cannot be made regretfully at the present. There was acknowledged a veryslight fall-down of the light output gradually toward said point D frompoint C possibly due to the excessive amount of gallium which will notreact with iodine to be kept in the form of the element vapour whichabsorbs radiated light. The output was fairly sharply decreased whengallium was added in further excessive amount.

The amount of gallium to be filled in the envelope of the discharge lampof this type generally and preferably ranges from 0.4 X to 4.0 X 10gram-atom per 1 cc. of the inner capacity of the envelope. Although saidlimits are not of course critical, when gallium to be added is leasserthan said lower limit the spectrum of gallium is apt to be considerablydecremented during the operation, while when it is more than said upperlimit the'discharge of the lamp is apt to be unstable. The inventorscarried out the other type of experiments in which the light outputswere determined in respect of the mercury lamps as referred to above,one of which had gallium and iodine filled in the gram-atom number ratioof 1:3 as in the recently developed lamp and the other of 1:1. When theamount of gallium was varied to obtain the respective curvesrepresenting light output characteristics of said two discharge lamps,it was found that said characteristic curves were substantiallycoincident with each other as illustrated in FIG.

2. As readily appreciated therefrom, the discharge lamp having theadditional filling of gallium and iodine in the ratio of 1:1 accordingto the present invention is not inferior at all to the lamp according tothe prior art of which envelope was filled additionally with gallium andhalide in the relative amount to form gallium triiodide.

Owing to the relatively lesser amount of iodine, the voltage necessaryfor starting the discharge lamp of the invention was about 700 V incomparison with 1,400 V of the lamp according to the prior art. Thereigniting voltage was also made fairly lower. it was confirmed alsothat such voltages were not almost raised different from the lamp of theprior art having gallium and iodine filled in the ratio of 1:3.

The similar results were observed also in respect of the mercury lamp inwhich bromine was used in stead of iodine.

What is claimed is:

1. In electric discharge lamps having a sealed envelope which provides apair of electrodes disposed therein and contains mercury and aninert-gas filled therein added with gallium and a halide selected fromeither of iodine and bromine, an improvement in that said gallium andsaid iodine are added in the gramatom number ratio of from 0.5 to 3.0.

2. Discharge lamps as claimed in claim 1, in which said gallium is addedin the amount of from 0.4 X 10' to 4.0 X 10' gram-atom per cubiccentimeter of the envelope inner capacity.

2. Discharge lamps as claimed in claim 1, in which said gallium is addedin the amount of from 0.4 X 10 6 to 4.0 X 10 6 gram-atom per cubiccentimeter of the envelope inner capacity.